Hydraulic pit prop



United States Patent 72] Inventors Karl Heinz Plester Wethmar near Lunen; Erich Hofl'mann, Altlunen, Westphalia, Germany [2]] Appl. No. 724,189 [22] Filed April 25, 1968 [45] Patented Dec. 1, 1970 [73] Assignee Gewerkschait Eisenhutte Westpfalia,

a body corporate of Germany [32] Priority April 29, 1967 [33] Germany [31 No. G37,060

[54] HYDRAULIC PIT PROP 2 Claims, 1 Drawing Fig. I [52] US. (31. 248/354, 248/407, 248/423: 254/ l 34 [51] Int. Cl E2ld 15/20 [501 Field of Search 248/354, 354(C), 354(H), 357, 407, 423; 254/133, 134, 133.1; 92/13 [5 6] References Cited UNITED STATES PATENTS 2,188,763 1/1940 Swan 254/134X 2,510,328 6/1950 Black 248/354X FOREIGN PATENTS Primary Examiner-Roy Frazier Assistant Examiner-Frank Domotor Attorney-Burgess, Dinklage & Sprung ABSTRACT: A pit prop having a variable effective length which is accomplished by mechanically resetting an extension member slidably mounted in an extended skirt of a piston member .which is in turn slidably mounted in a cylindrical outer member and displaced therein hydraulically. The extension member has grooves disposed along its periphery into one of which a split ring is located to abut the outer end of the skirt. A securing ring is attached to the skirt by means of a detachable locking element which extends through alined bores in the split ring, the skirt and the extension member. To vary the effective length of the pit prop the securing parts are detached and the split ring relocated in another groove of the extension member.

HYDRAULIC PIT PROP BACKGROUNDTQ THE INVENTION In order that a hydraulic pit prop may be utilised in various underground mine workings-in which there are substantial differences in the heights of the roof, it is considered advantageous to provide means for varying the effective length of the prop. Hydraulic pit props are available which have an extension which can be raised hydraulically, but such pit props are generally complicated and costly to manufacture. It is an object of the present invention to provide a pit prop having a variable effective length in which the effective length can be adjusted mechanically, but which at the same time achieves the advantages of hydraulic extension and retraction.

SUMMARY OF THE INVENTION f. a split ring located in one of said grooves and abutting the' outer end of the skirt portion, and g. a securing ring detachably secured to the skirt portion to Referring to the accompanying drawing, the hydraulic pit prop has a cylindrical outer member 13 closed at its lower end by a prop shoe l5 and having slidably received thereina piston member 14. The piston member 14 has an extended tubular skirt portion 1 into the open end of which an extension member 2 is slidably received. A passage 16 is provided in the prop shoe 15 for admitting hydraulic pressure into the space between the piston 14 and the cylindrical member 13 so as to extend the piston member, 14 hydraulically. A passage 17 is formed in the wall of the cylindrical member 13 for introducing hydraulic fluid into the space between the tubular skirt member] and the cylindrical outer member 13 and thus-to effect retraction of the piston member 14 and its associated skirt portion 1. This is normally referred to in the art as a robbing aid.

The peripheral surface of the extension member 2 is provided with a number of cylindrical grooves 3 spaced along its length. Just below each of the grooves 3, a transverse bore 7 is 5 formed in the extension member 2 andan additional transretain the split ring in p'osition, whereby the split ring and securing ring serve to secure the extension member to the piston member in alternative positions to vary the effective overall length of the prop. While various methods may be adapted for detachably securing the securing ring, it is advantageously secured to said tubular skirt by means of a locking pin or sleeve which extends through alined bores in the securing ring, the walls of the tubular skirt portion and said extension member.

In use, the outer end of the extension member is attached to a roof bar and the roof bar pressed against the roof of a mine working by admitting a hydraulic pressure fluid into the cylindrical outer member. The roof bar may be additionally supported by further associated hydraulic props .which maybe similar in construction to the hydraulic pit prop of the present invention. In order to vary the effective length of the pit prop, the piston member is retractedinto the outer member hydraulically by actuating what is normally known in the art as a robbing aid". The split ring can then be removed from the groove in which it is located by first. disconnecting the securing ring. The split ring can then be relocated in a different groove and the securing ring resecured. In this way, the effective length of the prop can, be lengthened or shortened. After renewed locking of the securing ring, the prop is once more ready for use. Thus, in accordance with the invention, it is possible to dispense with a separate hydraulic piston on the ex- 60 retraction and extension of the extension member mechanitension member without,however, the need for effecting cally. a

According to a further feature of the invention, the length of said tubular skirt portion isnot less than the length of the extension member so that in the position where the extension member is fully retracted relative to the skirt portion, the extension member is substantially .contained within the tubular skirt portion.

A BRIEF DESCRIPTION OF DRAWING One embodiment of a pit prop made in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawing, which is a part-sectional elevation of the pit prop. I i

verse bore 18 having the same dimensions as the bores 7 is drilled in the outer end of the extension member 2. A split ring 10 is received in one of the grooves 3 and is retained in position by means of a securing ring 9 which is itself locked to the outer end of the tubular skirt portion 1. As will be seen in the drawing, the securing ring 9 partially overlaps the split ring 10 and thus retains it in position. Because of the overlap of the securing ring 9, the split ring 10 cannot be drawn out above the securing ring 9 in use and undesired removal of the split ring 10 from the groove is, therefore, not possible. The securing ring 9 is locked to the outer end of the skirt portion 1 by means of locking means 8 which pass through alined bores 6 in the securing ring 9, bores 6 in the walls of skirt portion 1 and through the bore 7 in the extension member 2. In this way the extension member 2 is secured to the skirt portion 1 ofthe piston member 14 and consequently can be extended or retracted hydraulically with the piston member 14. It will be noted that the split ring 10 bears on the upper. end face of the skirt portion 1 so that when in use, the force exerted by the roof pressureis transmitted through the ring 10 and the end face 12 of the skirt portion 1, t

When it is desired to vary the effective length of the prop, this is readily achieved by retracting thepiston member 14 together with the extension member 2 and driving out the clamping sleeve means 8 whereupon the ring 9 can be lifted off and the split ring 10 removed. The ring 10 can then be located in another go groove, the securing ring 9 repositioned and the clamping sleeve 8 reinserted through the appropriate transverse bore 7 in the extension member 2.

The transverse bore 18 in the extension member 2 is positioned so that when the extension member 2 is fully inserted into the skirt member 1 and the clamping sleeve 8 driven into the transverse bore 18, the upper face 11 of the extension member 2 is flush with the upper end face 12 of the skirt portion 1.

It will be appreciated that the securing ring 9 apart from retaining the split ring 10in position, also serves to stiffen the outer end of the skirt portion 1 and therefore prevents the outerend of the skirt portion 1 from being distorted outwardly under the action of the roof pressure.

Theextension member 2 may be susceptible to breakage in the region of the weakened portion of the groove 3 and it may thus be desirable to use an appropriately shaped clamping ring (not shown) to reinforce the part of the member 2 located above and adjacent the groove 3.

It is also desirable to shape the mating faces of the groove 3 1. A hydraulically-operated pit prop comprising:

a. a cylindrical outer member;

b. a piston member slidably mounted in the outer member and being formed with an extended tubular skirt portion, which portion has coaxial bores extending transversely of the longitudinal axis thereof;

c. a hydraulic pressure source connectable to the inner space of the outer member to displace the piston member longitudinally thereof;

d. an extension member slidably mounted in the skirt portion of the piston member;

e. a plurality of grooves disposed in the peripheral surface of the extension member and spaced longitudinally thereof;

f. a plurality of bores in said extension member which bores extend transversely of the longitudinal axis of the extension member, each of said bores being disposed adjacent one of the grooves in said extension member;

g. a split ring located in one of said grooves and abutting the outer end of the skirt portion;

h. a securing ring serving to retain the split ring in position and having coaxial bores therein; and

i. a locking sleeve serving to detachably secure thesecuring ring to the tubular skirt portion, said sleeve extending through a series of alined bores composed of one of the bores in said extension member and the bores in the securing ring and the skirt portion whereby the locking sleeve, the split ring and the securing ring serve to secure the extension member to the piston member in alternative positions to vary the effective overall length of the prop.

2. A pit prop according to claim 1 in which the length of said tubular skirt portion is not less than the length of the extension member so that in the position where the extension member is fully retracted relative to the skirt portion the extension member is substantially contained within the tubular skirt portion. 

